偏振频域光学相干层析成像技术研究
文献类型：学位论文
| 作者 | 陈艳 |
| 文献子类 | 博士 |
| 导师 | 王向朝 |
| 关键词 | 光学相干层析成像 optical coherence tomography 偏振 polarization 光谱校准 spectral calibration 复共轭镜像 complex conjugate artifact 散斑噪声 speckle noise |
| 其他题名 | Research on Fourier Domain Polarization-sensitive Optical Coherence Tomography |
| 英文摘要 | 光学相干层析成像（Optical Coherence Tomography, OCT）是一种基于低相干光干涉的生物医学光学成像技术，具有非侵入、高分辨、可在体检测生物样品内部结构等优点。偏振OCT是OCT的功能性扩展技术，可同时获得样品的结构图像和偏振参数图像。与偏振时域OCT相比，偏振频域OCT具有高速高灵敏度等优势，是主流偏振OCT成像技术，在眼科、牙科、皮肤、心血管等领域得到广泛应用。随着应用技术的发展，如何提高偏振频域OCT的成像质量一直被广泛研究。但目前此领域仍存在光谱错位、复共轭镜像及散斑噪声等问题。光谱错位使系统点扩展函数展宽，降低纵向分辨率，同时降低偏振参数的计算精度。复共轭镜像导致系统成像深度减半。散斑噪声降低信噪比，使图像清晰度下降。本论文针对上述问题，围绕如何提高偏振频域OCT成像质量开展理论与实验研究，主要包括以下几项工作： 1. 针对光谱错位降低偏振参数计算精度的问题，通过理论分析与仿真计算，给出光谱错位量与偏振参数计算精度间的关系。在此基础上，提出两种光谱校准方法，分参数法与系数优化法。分参数法利用测得的多组波片的延迟量和快轴方位角分别校准波数缩放和波数平移，实现光谱错位的校准。对波片偏振参数的测量实验验证了该方法的有效性。系数优化法通过自动优化两路光谱之间波数的比例系数实现光谱校准，只需对简单样品进行一次成像。仿真和实验表明，与已有的峰值法相比，系数优化法对于高斯型和非高斯型光谱均可获得更高的校准精度。 2. 提出一种基于正弦相位调制B-M扫描的时间载波复频域偏振OCT技术。该技术将B-M扫描方式与正弦相位调制相结合，对样品进行横向扫描的同时，将正弦相位调制引入正交的两路干涉光谱中。分别对正交的两路光谱沿时间方向进行傅里叶变换，利用时间频谱信息重建复干涉信号，消除偏振频域OCT的复共轭镜像、自相干噪声及直流背景噪声，使成像深度加倍。与线性调制相比，该技术避免了灵敏度随横向扫描距离增加而降低的问题，提高了系统灵敏度和偏振参数计算精度。仿真结果表明，该技术在有效消除复共轭镜像、直流背景等噪声的同时，可高精度获得延迟量和快轴方位角，二者的计算误差平均值均小于2×10-3 rad。 3. 提出一种基于分光谱的散斑噪声抑制方法，有效提高了偏振频域OCT的成像质量。将测量获得的两路干涉光谱的全光谱分别分割为几个窄带光谱，将各窄带光谱的A-line信号进行平均合成计算，实现对散斑噪声的抑制。仿真结果验证了该方法的有效性。实验结果显示，利用该方法获得的鸡胸肉样品的强度图像、延迟量图像和快轴方位角图像的标准差分别降低了48.39%、35.20%和46.84%，图像的信噪比、对比度噪声比及平均等效视数均得到有效提高。; Optical coherence tomography (OCT) is a noninvasive, high-resolution imaging technology based on low coherence interferometry. It detects backscattered light to create cross-sectional and three-dimensional images of biological samples. Polarization-sensitive OCT (PS-OCT) is a functional extension of OCT, which provides additional polarization information of the sample. Compared with time domain PS-OCT, Fourier domain PS-OCT (FD-PS-OCT) is a promising imaging technique due to its high imaging speed and high sensitivity. Now it has been widely applied in biomedical fields such as ophthalmology, dentistry, dermatology and so on. To meet the accurate diagnostic demands in these applications, a lot of studies have been conducted to improve the image quality of FD-PS-OCT. However, FD-PS-OCT still suffers from the problems of wavelength misalignment, complex conjugate artifact and speckle noise. Wavelength misalignments generate a depth-dependent broadening of the point spread function and result in nonnegligible polarization artifacts. Complex conjugate artifacts decrease the available imaging depth range to half of the original range. Speckle noise reduces image contrast and makes tissue boundaries blurred. In order to solve the problems, several techniques for improving the image quality of FD-PS-OCT are studied. The main contents are as follows. 1. A theoretical and simulation analysis is performed on the relationship between the wavelength misalignment and the calculated error of polarization parameters. Based on the analysis, two spectral calibration methods are proposed, which are polarization parameter method and coefficient optimization method. The polarization parameter method measures several groups of retardation and fast axis orientation of a wave plate, and then calibrates the translational shifts and tilts of the wavelength misalignment through the measured retardation and fast axis orientation values, respectively. The wave plate experiments show a good performance of the method. The coefficient optimization method requires only one measurement of a simple sample, and then the calibration is achieved by automatically seeking the optimal calibration coefficient of wavenumber. Simulations and experiments show that, compared to the peak method, the coefficient optimization method is suitable for both Gaussian and non-Gaussian spectrums with a higher calibration accuracy. 2. A complex Fourier domain PS-OCT technique based on sinusoidal phase modulation and B-M scan is proposed. The sinusoidal phase modulation of a reference beam (M scan) is introduced into the horizontal and vertical interferograms while the probe beam scans over the sample (B scan). Then Fourier transform is performed on the two orthogonal modulated interferograms with respect to time and the temporal frequency spectrums are obtained. Based on the temporal frequency spectrums, the complex interferograms of the two channels are reconstructed. By the Fourier transform of the complex interferograms, the full range images are obtained. The technique expands the imaging depth by a factor of 2. Compared with the linear phase modulation, the technique avoids the problem of sensitivity fall-off along the transverse scan and improves the calculation accuracy of polarization parameters. The simulation results show that, the complex conjugate artifacts can be eliminated, and both the calculation errors of the retardation and the optical axis orientation are smaller than 2×10-3 rad. 3. A split-spectrum method to reduce speckle noise for FD-PS-OCT is proposed. The method splits the horizontal and vertical interferograms into several narrow spectrums. After the traditional OCT data processing, A-line signals corresponding to the narrow spectrums are obtained. Then the A-line signals are averaged to suppress speckle noise. Simulation and experiment results show that, the method improves the image quality effectively. After using the method to suppress the speckle noise in the chicken breast muscle images, the standard deviations of the intensity, retardation and fast axis orientation images reduce by 48.39%, 35.20% and 46.84%, respectively. And the signal-to-noise ratio, contrast-to-noise ratio and average equivalent number of looks are improved as well. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31101]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 陈艳. 偏振频域光学相干层析成像技术研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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